FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in accordance with the prior art. Wireless telecommunications system 100 comprises: wireless terminal 101, base stations 102-1, 102-2, and 102-3, wireless switching center 111, assistance server 112, location client 113, and Global Positioning System (“GPS”) constellation 121. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in well-known fashion.
The salient advantage of wireless telecommunications over wireline telecommunications is the mobility that is afforded to the users. On the other hand, the salient disadvantage of wireless telecommunications lies in that fact that because the user is mobile, an interested party might not be able to readily ascertain the location of the user.
Such interested parties might include both the user of the wireless terminal and remote parties. There are a variety of reasons why the user of a wireless terminal might be interested in knowing his or her location. For example, the user might be interested in telling a remote party where he or she is or might seek advice in navigation.
In addition, there are a variety of reasons why a remote party might be interested in knowing the location of the user. For example, the recipient of an E 9-1-1 emergency call from the wireless terminal might be interested in knowing the location of the wireless terminal so that emergency services vehicles can be dispatched to that location.
There are many techniques in the prior art for estimating the location of a wireless terminal. In accordance with some techniques, the location of a wireless terminal is estimated, at least in part, from signal measurements that are reported by the wireless terminal. The reported measurements are of signals measured by the wireless terminal that are transmitted by one or more base stations and, in some cases, by GPS satellites.
Wireless terminal 101 reports measurements to telecommunications system 100, which measurements can then be used for location estimation purposes. Independent of location estimation, however, terminal 101 monitors the strength of signals transmitted by multiple neighboring base stations, such as base station 102-1 through 102-3, in order to ensure that the terminal is always communicating with the base station that provides the strongest signal. If, at some point, another base station is found to provide a stronger signal, the call that involves the user of terminal 101 might need to be handed over to the other base station. Terminal 101 can then ask the system to initiate a handover. This technique is known as a “mobile-assisted handover” (MAHO).
In addition to other signals that provide connectivity for the wireless terminals, each of base station 102-1 through 102-3 also transmits a signal that is designed to be relatively tolerant of interference. Such signals are known by various names such as “pilots” in systems that are based on code division multiple access (CDMA), or “cell-specific reference signals” (CRS) in systems that are based on 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE). These reference-type signals can achieve greater interference tolerance because they carry very little information, essentially carrying the identity of the originating cell only.
The cell-specific reference signals enhance the detectability of signals from neighboring cells and make MAHO possible.